The present invention relates to electronic controllers for laser optical amplifiers, specifically, controllers having logarithmic amplifiers.
Rare earth doped optical amplifiers have emerged as the predominant optical signal amplification device in nearly every aspect of optical communication networks spanning from repeaters, pre-amplifiers and power boosters to wavelength division multiplexed (WDM) systems. These amplifiers are suitable for terrestrial, transoceanic, metro/access, cable television, and local area networks. The optical amplifier boosts the optical signal directly in the optical domain without the need for converting the signal into an electrical signal. As modern telecommunication networks increasingly require robustness, flexibility, reconfigurability, and reliability, there is an ever-growing demand for automatically controlled optical amplifier devices.
In reconfigurable dense wavelength multiplexed (DWDM) systems with optical add-drop multiplexing (OADM), the input signal power undergoes variations as the channel configurations or the operation conditions change. It would be beneficial to provide a stabilized optical amplifier device that automatically adjusts its signal gain, or its signal output power. Furthermore, it would be beneficial to have an optical amplifier which can be dynamically controlled and adjusted by a central system via a standard communication port.
Laser diode driver circuits are required in optical telecommunication systems. Such circuits have been widely implemented in current optical systems primarily in two cases: (1) to drive optical signal transmitter lasers, such as distributed feedback (DFB) lasers and tunable laser diodes (TLD); and (2) to drive 980 nanometer or 1480 nanometer pump laser diodes for optical amplifiers, including erbium doped fiber amplifiers (EDFA) and Raman amplifiers.
Most of the currently deployed pump laser diodes and associated laser diode driver circuits are non-controllable. With increasing awareness of the importance of more reliable and more resilient optical networks, there have been efforts to develop controllable and programmable laser diode drivers, examples of which are shown in U.S. Pat. Nos. 5,604,757; 5,802,089; 5,675,600; and 6,055,252. While the laser diode controllers disclosed in these patents are controllable and offer improved performance and stability over non-controllable laser diodes, none of the controllers described therein are designed specifically for advanced optical amplifier applications. To implement such a dynamically controlled optical amplifier design, it would be beneficial to provide an electronic driver circuit that provides to the pump laser diode an adjustable driver current and that monitors the optical amplifier input and output signals.
Further, known electronic driver circuits provide one of gain clamping and output power clamping. It would be beneficial to provide an electronic driver circuit that can alternately provide both gain clamping and output power clamping.
Briefly, the present invention provides a dual mode electronic amplifier controller. The controller comprises a first amplifier electronically connectable to an optical input signal and a second amplifier electronically connectable to an optical output signal. The first amplifier has a first output and the second amplifier has a second output. The amplifier controller also comprises a microprocessor electronically connected to the first and second outputs. The microprocessor is adapted to operate in one of a first mode wherein the microprocessor compares functions of the first and second outputs and generates a first microprocessor output, and a second mode wherein the microprocessor compares the second output to a predetermined value and generates a second microprocessor output, such that, in either the first or second modes, each of the first and second microprocessor outputs is adapted to adjust electrical current to a laser.